The present invention relates to labeled compounds and more particularly to isotopically enriched acetic acid, (dialkylamino)oxo-, alkyl esters labeled with carbon-13 or with carbon-13 and hydrogen-2.
Diethyloxalate is an extremely useful synthon for the synthesis of many important biochemicals and pharmaceuticals. It can be used as a labeling synthon but has limitations in that it can only be used as a symetrically labeled compound. A new synthon has now been developed that has the synthetic utility of diethyl oxalate and allows the differentiation of each of the carbons.
It is an object of the present invention to provide labeled compounds useful for synthetic chemistry development.
In accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides labeled compounds of the formula 
where each C* is selected from the group consisting of a carbon-12, i.e., 12C, or a carbon-13, i.e., 13C and at least one C* is 13C, R1 is selected from the group of C1-C4 lower alkyl and aryl, and X is selected from the group of xe2x80x94NR2R3 where R2 and R3 are each independently selected from the group of C1-C4 lower alkyl, alkoxy and aryl, xe2x80x94SR4 where R4 is selected from the group of C1-C4 lower alkyl, alkoxy and aryl, and xe2x80x94OR5 where R5 is selected from the group of C1-C4 lower alkyl, alkoxy and aryl with the proviso that when R1 is methyl then R5 is other than methyl, when R1 is ethyl then R5 is other than ethyl, and when R1 is benzyl then R5 is other than benzyl. In specific embodiments, the labeled compounds include [1-13C]acetic acid, (dimethylamino)oxo-, ethyl ester, [2-13C]acetic acid, (dimethylamino)oxo-, ethyl ester, and [1,2-13C2]acetic acid, (dimethylamino)oxo-, ethyl ester.
The present invention is concerned with diethyl oxalate analogs useful for assymetric labeling of synthetic compounds. Generally, the compounds are labeled with carbon-13, although they may be labeled with deuterium (2H) as well.
Particularly, the present invention is concerned with labeled compounds of the formula 
where each C* is selected from the group consisting of a carbon-12, i.e., 12C, or a carbon-13, i.e., 13C and at least one C* is 13C, R1 is selected from the group of C1-C4 lower alkyl and aryl, and X is selected from the group of xe2x80x94NR2R3 where R2 and R3 are each independently selected from the group of C1-C4 lower alkyl, alkoxy and aryl, xe2x80x94SR4 where R4 is selected from the group of C1-C4 lower alkyl, alkoxy and aryl, and xe2x80x94OR5 where R5 is selected from the group of C1-C4 lower alkyl, alkoxy and aryl with the proviso that when R1 is methyl then R5 is other than methyl, when R1 is ethyl then R5 is other than ethyl, and when R1 is benzyl then R5 is other than benzyl.
As used herein, the term xe2x80x9clower alkylxe2x80x9d refers to C1-C4 alkyl such as methyl, ethyl, n-propyl, iso-propyl, butyl, isobutyl, and tert-butyl while the term xe2x80x9carylxe2x80x9d means a monovalent monocyclic or bicyclic aromatic hydrocarbon radical of 6 to 10 ring atoms, and optionally substituted independently with one, two, three, four or five substituents selected from alkyl, haloalkyl, cycloalkyl, halo, nitro, cyano, xe2x80x94OR (where R is hydrogen, alkyl, haloalkyl, cycloalkyl, optionally substituted phenyl), acyl, and xe2x80x94COOR (where R is hydrogen or alkyl). More specifically, the term xe2x80x9carylxe2x80x9d includes, but is not limited to 1-naphthyl, substituted 1-naphthyl, 2-naphthyl, substituted 2-naphthyl, and phenyl groups with the structure 
wherein R11, R12, R13, R14 and R15 are each independently a lower alkyl, i.e., a C1-C4 alkyl such as methyl, ethyl, n-propyl, iso-propyl, butyl, isobutyl, and tert-butyl, a halogen such as chloro, bromo or iodo, an amino group such as NH2, NHR or NRRxe2x80x2 where R and Rxe2x80x2 are each a lower alkyl or aryl as described above, or an alkoxy group such as O-alkyl or O-aryl where the alkyl is a lower alkyl as described above or an aryl as described above. Additionally, the aryl group may be a benzyl group.
Among particular labeled compounds are included [1-13C]acetic acid, (dimethylamino)oxo-, ethyl ester, [2-13C]acetic acid, (dimethylamino)oxo-, ethyl ester, and [1,2-13C2]acetic acid, (dimethylamino)oxo-, ethyl ester.
Each of these labeled compounds can be synthesized from similar starting materials, e.g., methyl phenyl sulfide.
In an exemplary process of the present invention, C*O2 where C* is 12C or 13C is reacted with a [12C or 13C]methyl phenyl sulfide to form an addition product, a chlorination reaction is conducted with the addition product to form an acid chloride-containing intermediate, an exchange reaction is conducted between dimethyl amine and the acid chloride-containing intermediate, and reaction with thionyl chloride is conducted followed by reaction with an ethanol-water mixture to yield the labeled compound.
Unlike labeled diethyl oxalate, the reactivity of the labeled acetic acid, (dimethylamino)oxo-, ethyl esters can be tailored to produce a variety of labeled biochemicals and pharmaceuticals with predictable regioselectivity. For example, a general reaction for the production of isotopically labeled glycerol using such a reagent can be as follows.
Lithium methyl phenyl sulfide can be reacted with any one of the described labeled acetic acid, (dimethylamino)oxo-, ethyl esters in THF to form an intermediate product. Such an intermediate product can then be reacted with diisobutylaluminum hydride (DIBAL) followed by reaction with acetic anhydride and sodium acetate and followed by reaction with lithium borohydrate to form differently labeled glycerols. In the case of [1-13C]acetic acid, (dimethylamino)oxo-, ethyl ester as a starting material, the product will be [1,3-13C2]glycerol. In the case of [2-13C]acetic acid, (dimethylamino)oxo-, ethyl ester as a starting material, the product will be [1,2-13C2]glycerol. In the case of [1,2-13C2]acetic acid, (dimethylamino)oxo-, ethyl ester as a starting material, the product will be [U-13C3]glycerol.
The present invention is more particularly described in the following examples which are intended as illustrative only, since numerous modifications and variations will be apparent to those skilled in the art.